1. Field of the Invention
The present invention relates to a magnetic head for perpendicular magnetic recording that is used for writing data on a recording medium by means of a perpendicular magnetic recording system, and more specifically, to a magnetic head for perpendicular magnetic recording that has a main pole and a return path section.
2. Description of Related Art
The recording systems of magnetic read/write apparatuses include a longitudinal magnetic recording system wherein signals are magnetized in a direction along the plane of the recording medium (the longitudinal direction) and a perpendicular magnetic recording system wherein signals are magnetized in a direction perpendicular to the plane of the recording medium. It is known that the perpendicular magnetic recording system is harder to be affected by thermal fluctuation of the recording medium and capable of providing higher linear recording density, compared with the longitudinal magnetic recording system.
Magnetic heads for perpendicular magnetic recording typically have, like those for longitudinal magnetic recording, a structure where a read head section having a magnetoresistive element (hereinafter, also referred to as MR element) for reading and a write head section having an induction-type electromagnetic transducer for writing are stacked on the top surface of a substrate. The write head section includes a main pole that produces a write magnetic field in a direction perpendicular to the plane of the recording medium. The main pole includes, for example, a track width defining portion having an end located in a medium facing surface that faces the recording medium, and a wide portion that is connected to the other end of the track width defining portion and is greater in width than the track width defining portion. The track width defining portion has a generally constant width. To achieve higher recording density, it is required that the write head section of the perpendicular magnetic recording system be smaller in track width and improved in write characteristics such as overwrite property which is a parameter indicating an overwriting capability.
A magnetic head for use in a magnetic disk drive such as a hard disk drive is typically provided in a slider. The slider has the medium facing surface mentioned above. The medium facing surface has an air inflow end (a leading end) and an air outflow end (a trailing end). The slider is designed to slightly fly over the surface of the recording medium by means of an airflow that comes from the air inflow end into the space between the medium facing surface and the recording medium.
Here, the side of positions closer to the leading end relative to a reference position will be defined as the leading side, and the side of positions closer to the trailing end relative to the reference position will be defined as the trailing side. The leading side is the rear side in the direction of travel of the recording medium relative to the slider. The trailing side is the front side in the direction of travel of the recording medium relative to the slider.
The magnetic head is typically disposed near the trailing end of the medium facing surface of the slider. In a magnetic disk drive, positioning of the magnetic head is performed by a rotary actuator, for example. In this case, the magnetic head moves over the recording medium along a circular orbit about the center of rotation of the rotary actuator. In such a magnetic disk drive, a tilt of the magnetic head with respect to the tangent of the circular track, which is called a skew, occurs according to the position of the magnetic head across the tracks.
In particular, in a magnetic disk drive of the perpendicular magnetic recording system which is higher in capability of writing on a recording medium than the longitudinal magnetic recording system, the skew mentioned above can cause the phenomenon that signals already written on one or more tracks that are adjacent to a track targeted for writing are erased or attenuated during writing of a signal on the track targeted for writing (such a phenomenon will hereinafter be referred to as adjacent track erasure). For higher recording densities, it is necessary to prevent adjacent track erasure.
Providing one or more shields near the main pole is effective for preventing adjacent track erasure induced by the skew mentioned above and increasing the recording density. For example, U.S. Patent Application Publication Nos. 2005/0128637 A1 and 2010/0165517 A1 each disclose a magnetic head including a shield having an end face that is located in the medium facing surface to wrap around an end face of the main pole.
A magnetic head including one or more shields is typically provided with one or more return path sections including the one or more shields. The one or more return path sections are magnetically connected to part of the main pole away from the medium facing surface. The one or more return path sections have the function of capturing a magnetic flux that is produced from the end face of the main pole and spreads in directions other than the direction perpendicular to the plane of the recording medium, so as to prevent the magnetic flux from reaching the recording medium. The one or more return path sections also have the function of allowing a magnetic flux that has been produced from the end face of the main pole and has magnetized the recording medium to flow back to the main pole. Thus, the magnetic head having one or more shields near the main pole can prevent the occurrence of adjacent track erasure and provide a further improved recording density.
U.S. Patent Application Publication Nos. 2005/0128637 A1 and 2010/0165517 A1 each disclose a magnetic head including, as the aforementioned one or more return path sections, a return path section located on the leading side relative to the main pole and a return path section located on the trailing side relative to the main pole.
Now, the configuration of the return path section located on the trailing side relative to the main pole (hereinafter, referred to as the trailing return path section) will be contemplated. In a magnetic head, the read head section and the write head section stacked on the top surface of the substrate are typically located on the trailing side relative to the top surface of the substrate. In this case, the trailing return path section is disposed farther from the top surface of the substrate than is the main pole. The main pole and the trailing return path section define a space through which a portion of a coil passes. In such a magnetic head, the trailing return path section is typically composed of a plurality of layers.
In the magnetic head shown in FIG. 9 of U.S. Patent Application Publication No. 2005/0128637 A1, the trailing return path section is composed of a shorting shield, a return pole, a back via and a yoke. In this magnetic head, the shorting shield is extremely longer in the direction of travel of the recording medium than in the direction perpendicular to the medium facing surface, and an end face of the shorting shield is exposed over a large area in the medium facing surface. When the shorting shield has such a configuration, part of the magnetic flux captured into the shorting shield from a part of the end face of the shorting shield located near the end face of the main pole may leak from another part of the end face of the shorting shield toward the recording medium. This may result in the occurrence of adjacent track erasure.
Furthermore, in the above-described magnetic head, heat generated by the coil may cause expansion of the shorting shield and an insulating layer surrounding the coil, and thereby cause the end face of the shorting shield to protrude toward the recording medium. The protrusion of the end face of the shorting shield causes the end face of the main pole and an end of the read head section located in the medium facing surface to get farther from the recording medium, and this may result in degradation of the read and write characteristics.
In the magnetic head shown in FIG. 2 of U.S. Patent Application Publication No. 2010/0165517 A1, the trailing return path section is composed of seven layers. The seven layers include a top shield layer having an end face that is located in the medium facing surface at a position on the trailing side relative to the end face of the main pole, and second to fourth layers that are stacked in order on the top shield layer. In this magnetic head, each of the second to fourth layers has an end face that is closer to the medium facing surface and located at a distance from the medium facing surface. This magnetic head can avoid the problems resulting from a configuration in which an end face of the trailing return path section is exposed over a large area in the medium facing surface.
However, the magnetic head shown in FIG. 2 of U.S. Patent Application Publication No. 2010/0165517 A1 has the following drawback. In this magnetic head, the end face of the top shield layer located in the medium facing surface and the top surface of the top shield layer intersect at 90°. Consequently, the trailing return path section has an edge with an angle of 90° in the vicinity of the medium facing surface. When the trailing return path section has such a configuration, there tends to be magnetic field leakage from the vicinity of the aforementioned edge to the outside of the trailing return path section. This may result in the occurrence of adjacent track erasure.